Bonding aluminum to titanium and heat treating the composite



United States Patent Ofitice 3,359,142 Patented Dec. 19, 1967 3,359,142 BONDING ALUMINUM T TITANIUM AND HEAT TREATING THE COMPOSITE Bennie Ray Ward, Jr., Chesterfield County, Va., assignor to Reynolds Metals Company, Richmond, Va., a corporation of Delaware No Drawing. Filed Oct. 18, 1965, Ser. No. 497,554 6 Claims. (Cl. 148-115) This invention relates to novel composites having both titanium and aluminous metal components. More particularly, the invention concerns bonded composites of heat-treatable aluminum base alloys and heat-treatable titanium alloys in the solution heat treated condition,

which possess high resistance to deformation and to corrosion.

Composites of titanium and aluminum find limited application in aircraft structures, especially where light weight, rigidity and corrosion resistance are of importance.

In accordance with the present invention there are provided novel composites of aluminum base alloys and heattreatable titanium alloys which possess the foregoing properties in greater degree than known composites of titanium and aluminum.

The term aluminous metal refers to alloys which contain at least 50% aluminum. Aluminum base alloys which may be advantageously employed in accordance with the invention include heat-treatable wrought alloys of the aluminum-copper or the aluminum-zinc-magnesium types, such as copper-bearing alloys 2014, 2017, 2024, and 2025, ranging in copper content from about 3.5% to about 5.0%, and zinc-bearing alloys such as 7075 and 7002, the strength of which is increased by solution heat treatment (810990 F.) followed by quenching, and aging.

The aluminum base alloys may also be used when clad on at least one side with aluminum, for example alclad 2024 with a 2.5% or a 5% cladding.

Heat-treatable titanium alloys which are advantageously employed in the composites of the invention include the heat-treatable alloys of titanium with aluminum and vanadium or molybdenum. These may be used in the form of sheet or mesh. They are preferably employed in the solution heat treated condition, or in the solution heat treated and aged condition.

Examples of suitable heat-treatable titanium alloys of the type described aretitanium alloyed with 6% aluminum and 4% vanadium, and titanium alloyed with 4% aluminum, 3% molybdenum and 1% vanadium. These titanium alloys are particularly adapted to bonding with aluminum alloys which are responsive to thermal treatment within approximately the same temperature range as the titanium alloys themselves. The alloys are available as sheet in the cold rolled or cold drawn condition. Solution heat treatment of the titanium alloys increases their tensile strength from 1l 0l50K s.i. to above 180K s.i.

K when aged at about 900 F.

In the preparation of the composites of the invention, the sheets of aluminum and of titanium alloy may be of any desired thickness compatible with good bonding, varying from foil gages up to the limit of the processing equipment. Preferred aluminum alloy gages vary, for example, from 0.040 inch to 0.125 inch, while suitable titanium alloy gages may range from 0.02 to 0.05 inch, all before bonding. These gage ranges are to be considered as illustrative, however, and not as limiting.

The composites of the invention may be bonded by rolling or by means of suitable adhesives, but rolling is preferred. Bonding is advantageously performed by a rolling operation in which the titanium alloy sheet is maintained substantially at room temperature. The aluminum alloy is preheated to a temperature between about 650 F. and about 1000 F., depending upon the alloy employed, care being taken to avoid grain boundary melting. A temperature range between about 850 F. and about 950 F. ordinarily is preferred. The time of preheat may vary according to conditions, but generally a period of from 5 to 15 minutes is sufficient to uniformly heat the aluminum to the desired temperature. The time of preheat should, however, be kept to a minimum because of surface oxidation.

The metal-to-metal composites of the invention may be of the binary type, i.e. a single layer of aluminum alloy bonded to a single layer of titanium alloy, or they may be of the sandwich type, such as a layer of aluminum alloy between two layers of titanium alloy. Where alclad alloy is used, the titanium alloy is preferably bonded to the aluminum cladding layer. Also included within the scope of the invention are composites having adjacent multiple thicknesses of one or both of the titanium alloy and aluminous metal components.

In preparing the composites of the invention, the surface of the aluminum or aluminum base alloyis degreased, and is then roughened by wire brushing, sanding, grinding, or like methods, in order to remove any film or thin layer of aluminum oxide which would interfere with bonding. If desired, a chemical dip may also be employed. Similarly, the titanium alloy is subjected to roughening by brushing, or by grinding, to break up any oxide layer.

As mentioned previously, bonding may be by means of an adhesive or by rolling. Where rolling is used, the production of a bond may be effected with a reduction in the thickness of the aluminum alloy sheet from about 30% to about 70%, and in the titanium alloy sheet from about 10% to about 50%. Rolling is carried out in conventional equipment, an overall gage reduction of about 50% resulting in satisfactory bonding.

After bonding, the composite is subjected, in accordance with the invention, to a thermal treatment by reheating the bonded composite to a temperature between about 850 F., and about 950 F. for a period of from about 30 minutes to about 2 hours or more. This serves to strengthen the titanium alloy and to solution heat treat the aluminum alloy. The temperature is selected according to the particular alloys involved. Thus, for example, alloy 2024 requires treatment at about 920 F., while alloy 7075 is heated at about 880 F. Followed by a cold water quench, such thermal treatment places the aluminum alloy in T4 temper condition, while if followed by a cold water quench and precipitation hardening (aging) it places the aluminum alloy in T-6 temper condition.

The following examples serve to illustrate the practice of the invention, but are not to be considered as limiting:

I Example 1 A composite was prepared from a sheet of annealed alclad 2024 alloy, clad on one side with aluminum, dimensions 6" x 6" x 0.080", and sheet of Ti6Al-4V sheet, solution heat treated at 1650 F. and cold water quenched, dimensions 6" x 6" x 0.045". Prior to bonding, both pieces were wire brushed on the side to be bonded. The 2024 sheet was heated for 10 minute at 900 F., and the titanium alloy sheet was maintained at room temperature. The sheets were bonded by rolling in a 4-high mill having work rolls 8" in diameter, back-up rolls 16", width 18", using a mill setting of -0.010" (negative roll gap) to effect an approximately 50% reduction. The bonded composite (51% 202449% Ti-6Al-4V) exhibited the following properties in the as-rolled condition: Tensile strength 117K s.i., yield strength 98.8K s.i., percent elongation in 2":4. The composite then was heat treated at 910 F. for 2 hours and quenched in cold water.

The composite exhibited longitudinally a tensile strength of 121,900 p.s.i., a yield strength of 109,600 p.s.i., an elongation in 2 inches of 6.5%.

Example 2 Proceeding as in Example 1, a composite was prepared from a sheet of annealed alclad 2024 alloy, dimensions 6" x 7" x 0.080", and a sheet of Ti-4Al-3Mo-1V, dimensions 6" x 6" x 0.032 solution heat treated at 1650 F. for 15 minutes and cold water quenched. Both pieces were wire brushed on one side before bonding. Prior to bonding the 2024 sheet was heated for 10 minutes at 850 F. while the titanium alloy was kept at room temperature. Bonding was performed using a mill setting of plus 0.010".

The bonded composite (64% 202436% Ti4Al-3Mo- 1V) exhibited the following properties in the as-rolled condition: Tensile strength 93.6K s.i., yield strength 80.6K s.i., percent elongation in 2"=5.3. Upon heating the compositeat 910 F. for various times and quenching in cold water the following properties were obtained:

10.5. in K s.i. Y.S. in K s.i. Percent E1.

1 hour at 910 F 104.5 5.0 2 hours at 910 F. 108.0 89 .8 12 .0 4 hours at 910 F 103.0 90.9 4.0 8 hours at 910 F 110.2 91.4 5.0

Example 3 A composite was prepared from a sheet of annealed Alclad 7075 alloy, dimensions 6" x 7" x 0080",, and a sheet of Ti-6Al-4Mn, dimensions 6" x 6" x 0.045", solution heat treated at 1650 F. for 30 minutes and cold water quenched. Both pieces were wire brushed on one side before bonding. Prior to bonding the 7075 sheet was heated for 10 minutes at 850 F., while the titanium alloy was kept at room temperature. Bonding was performed using a mill setting of 0.010 (negative roll gap).

The bonded composite (50% 707550% Ti-6Al-4V) exhibited the following properties in the as-rolled condition: Tensile strength 127.1K s.i., yield strength 111.8K s.i., percent elongation in 2"=6.0. Upon heating the composite at 880 F. for various times, quenching in cold water, incubating for days at room temperature and aging at 250 F. for 24 hours the following properties are obtained:

T.S. in K s.i. Y.S. in K s.i. Percent E1.

1 hour at 880 F 133 .4 102.7 5.0 2 hours at 880 F. 135.0 102 .0 6.0 4 hours at 880 1*. 131 .2 97 .2 5.0 8 hours at 880 F 132 .2 100 .7 4.0

Example 4 4 3MolV) exhibited the following properties in the as-rolled condition: Longitudinal tensile strength 983K s.i., yield strength 775K s.i., percent elongation in 2":6; transverse tensile strength 96.7K s.i., yield strength 71.8K s.i., percent elongation in 2: 15.5.

Upon heating the composite at 880 F. for various times, quenching in cold water, incubating for five days at room temperature, and aging at 250 F. for 24 hours the following properties were obtained:

What is claimed is:

1. The method of producing a metal composite, comprising the steps of:

bonding a layer of heat-treatable aluminous metal to a layer of titanium alloy which is susceptible to strengthening by a thermal treatment in the temperature range for solution heat treatment of the aluminous metal; and

heating the bonded layers so as to effect concurrently a solution heat treatment of said aluminous metal and the strengthening of said titanium alloy.

2. The method of producing a metal composite, comprising the steps of:

bonding a layer of heat-treatable aluminous metal to a layer of solution heat-treated titanium alloy;

heating the bonded layers so as to effect concurrently a solution heat treatment of the aluminous metal and the strengthening of said titanium alloy; and quenching the bonded layers.

3. The method of claim 2, including bonding a layer of Alclad aluminum base alloy to a layer of solution heattreated titanium alloy, by rolling said layers in direct contact, with the clad surface of said aluminum base alloy against the titanium alloy.

4. The method of claim 2, including the step of aging the bonded layers to effect precipitation hardening of the aluminous metal.

5. The method of producing a metal composite, comprising the steps of:

providing a layer of heat-treatable aluminum base alloy and a layer of solution heat-treated titanium alloy compatible therewith both for bonding by rolling and for subsequent solution heat treatment of the aluminum base alloy, said titanium alloy being susceptible to strengthening by a thermal treatment in the temperature range for solution heat treatment of the aluminum base alloy;

rolling said layers to form a bonded composite; and

heating the composite so as to effect concurrently a solution heat treatment of said aluminum base alloy and the strengthening of said titanium alloy.

6. The method of claim 5 in which said rolling step includes preheating the aluminum base alloy in the temperature range from about 650 F. to about 1000 F.

HYLAND BIZOT, Primary Examiner, 

1. THE METHOD OF PRODUCING A METAL COMPOSITE, COMPRISING THE STEPS OF: BONDING A LAYER OF HEAT-TREATABLE ALUMINOUS METAL TO A LAYER OF TITANIUM ALLOY WHICH IS USCEPTIBLE TO STRENGTHENING BY A THERMAL TREATMENT IN THE TEMPERATURE RANGE FOR SOLUTION HEAT TREATMENT OF THE ALUMINOUS METAL; AND HEATING THE BONDED LAYERS SO AS TO EFFECT CONCURRENTLY A SOLUTION HEAT TREATMENT OF SAID ALUMINOUS METAL AND THE STRENGTHENING OF SAID TITANIUM ALLOY. 